In recent years, the integration of Blockchain technology into the IoT has led to the development of robust and significant security solutions, most prominently for distributed and secure authorisation methods in IoT networks. Due to the numerous potential benefits of Blockchain technology, including decentralisation, immutability, consensus-mechanism, transparency, accessibility, autonomy, and accountability, a number of research studies are focusing on resolving a variety of issues associated with existing authorisation mechanisms for IoT devices, such as a single point of failure, data and policy tampering, insufficient control and transparency, and scalability. For instance, the initial Blockchain-based proposals [1]} [2]} [3]} [4]} for device authorisation in decentralised IoT environments are focused on resolving issues of a single point of failure and policy tampering by storing all access control policies as transactions on the distributed immutable ledger and enforcing all access control policies via the service providers. Furthermore, with the utilisation of smart contract features in designing the authorisation schemes for IoT, the authors in [5]} [6]} [7]} presented the access control schemes that exploit the Blockchain's smart contract capabilities to execute the access control policies automatically and to further achieve transparency by maintaining and storing access permissions on the different Blockchains such as public and private. Similarly, Hossein et al. [8]} presented an access control mechanism for IoT that employs a distributed tempered-proof feature of Blockchain to store access rights. Furthermore, Novo [9]} presented a Blockchain-based distributed architecture for storing arbitrating roles and access control permissions on Blockchain to address the scalability problem of managing access to restricted devices in the IoT environments.
